In "A High-Resolution Laser-Based Deflection Measurement System for Characterizing Aluminum Electrostatic Actuators" (Proceedings of Transducers 1995; Stockholm, Sweden; pp. 308-311), testing of torsional aluminum actuators for angular deflection and dynamics using standard benchtop optics is described. Laser light is produced by a He--Ne laser with a 500 .mu.m beam diameter and is directed through an attenuator, a beam splitter, and a lens that focuses a spot onto an actuator surface. Light reflected from the actuator surface passes back through the lens and is diverted by the beam splitter onto two photodiodes positioned 100 .mu.m apart. Upon actuation, the spot position with respect to the position of the two photodiodes is detected as a difference in illumination between the two photodiodes. Spot movement is a function of actuator angular rotation and the focal length of the lens. Standard optical and electronic methods are used to deduce the voltage sensitivity and dynamic response of the actuator from measurements of the movement of the spot.
Testing of a micro-machined mirror at an individual component level could be done in a manner very similar to what is described in this paper. However, the drawback is that in order to test each mirror chip, the chip would need to be mounted on a suitable fixture that provides a means to supply the mirror's actuation signal. This fixture would then mounted such that a deflectable surface of the mirror was aligned correctly with respect to the incoming laser beam. The mirror would then be tested and if it met specifications it could be assembled as part of an optical head of an optical data storage and retrieval system and if not acceptable it would be discarded. Testing in this manner would be slow, tedious, and would subject the mirror chips to considerable handling risk which would be compounded by the fragile nature of the mirror's deflectable plate and the very small size of the chip itself (as for example 0.7 mm.times.1.5 mm). To date, the use of micro-machined mirrors in a commercial optical data storage product is not known. Hence, a need for high volume manufacturing and testing of micro-machined mirrors has not been necessary.
Probe control stations equipped with device-specific probe cards are used in the semiconductor industry for the wafer level testing of integrated circuits. These machines allow for the rapid and automated testing of a plurality of circuits patterned onto a wafer. Devices tested in this manner can be rejected and appropriately marked at the wafer level if they don't perform to specifications, thus, simplifying the sorting of good from bad parts. Connection to a computer allows for the transfer and storage of the test results for later retrieval and analysis. Such systems have been typically applied to electrical testing of discrete semiconductor devices or semiconductor integrated circuits.
What is needed is a method for testing the electrical-optical-mechanical performance of micro-machined parts at the wafer level in a manner that is compatible with the high volume manufacturing procedures.